1. Field of the Invention
The subject matter of the invention is directed to a process for the production of hydroxylamine disulfonate diammonium salt (DS) and the effective control of said process.
2. Description of Related Art
Hydroxylamine is widely useful in the transformation of organic compounds to derivatives, which in turn may be intermediates in pharmaceutical or other industrial synthesis of complex molecules. An important use of hydroxylamine is captively in the synthesis of caprolactam, the raw material for nylon 6.
The classical method for the production of hydroxylamine is that ascribed to Raschig. An important commercial process consists of the reduction of ammonium nitrite with ammonium bisulfite and sulfur dioxide to give hydroxylamine disulfonate diammonium salt (DS). Upon hydrolysis, DS gives hydroxylamine sulfate, an intermediate in the production of caprolactam. The overall reaction for production of DS is: ##STR1## where NH.sub.4 HSO.sub.3 is produced from SO.sub.2 and a basic ammonium compound: EQU NH.sub.4 OH+SO.sub.2 .fwdarw.NH.sub.4 HSO.sub.3. (2)
In commercial practice, the reaction is conducted in a packed tower or column where a solution of the product is recirculated, an aqueous nitrite solution is fed to the recirculating product stream, and supplemental trim ammonia, such as ammonium hydroxide or ammonium carbonate or bicarbonate is added in an amount to satisfy the stoichiometric requirements NO.sub.2.sup.- /NH.sub.4.sup.+ =1/2, and SO.sub.2 gas, obtained for example by combustion of sulfur with air, is fed at the bottom of the packed column and is vigorously contacted with the liquid in the packed section of the tower.
The amount of SO.sub.2 fed to the tower should also satisfy the requirements of equation (1) above and the three reactants should therefore be fed in the molar proportions NO.sub.2.sup.- /NH.sub.4.sup.+ /SO.sub.2 =1/2/2.
However, in plant practice it has been found that controlling the reaction in this manner by controlling the feed for reactant ratios is not feasible since unexpected fluctuations of concentrations in liquid and gas streams occur often in the feed to the packed tower.
The reaction is complex, with the possibility of many side reactions which have been discussed authoritatively in a review by F. Seel, Fortschr. Chem. Forsch. 4, 301-332 (1963).
It is desirable, therefore, to develop an effective control method to control the process for production of DS.